ASHRAE Journal

AIVC #13,671

'

Ventilation for Enclosed

Parking Garages By Moncef Krartt, Ph.D., P.E., and Arselene Ayarl, Ph.D.

Member ASHRAE

Automobile I arkin!!garage an be partially open or fully enclosed.

Partial I pen l:!arng s ar typically above-grade \Vith open sides and g ncrall d n t n d mechanical ventilation. However, folly

enclosed parking garages arc usually underground and require mechanical ventilation. Indeed. in the absence of ventilation. cndoscJ parking facilities present several indoor air qua I ity problems. The most serious is the emission of high levels ofcarbon monoxide ((0) by cars within the parking garages. Other concerns related to endoscd gar..iges arc the presence ofoil and 1.rnsolinc fumes. and other contaminant-; such as oxides of nitrogen (NO ) - - \ and smoke haze from diesel engines.

To dttcrmine the adequate ventilation rate for garages, two factors arL' typically .:unsidereJ: the number of car in operation and the emission quantities. The number of cars in operation depends on the type of thl! facility served by the parking garage and may vary from 3';, (in shopping an.:as) up to 20''o (in sports stadiums) of the total vchick capacity. The emission of carbon monox idc depends on individual cars including factors such as the age of the car. the engine power. and the level of car maintenance.

For enclosed parking facilities. ANSI! ASllRAE Standard 62-1989. 1;:111ilutio11 /i1r Acceptahle Indoor Air ()uafii specifics a fixed vcntih1tion rate of below 7.62 L/sm' ( 1.5 ct'rn/fl') of gross floor area.: Therefore, a ventilation flow of about 11.25 air changes per hour is required for garages with 2 5 m (8 ft) ceil ing height.

However. some of the model code authorities speei ty an air change rate of four to six air changes per hour. In addition. some of the modi:! code au1horities allow the ventilation rat.: to \ary and be reduced to sa vc fan energy if CO-demand con1rol lcd ventilation is pertl11mcd. that

is. a continuous monituring of CO concentrations is conducrcJ. with the monitoring system being interlm:ked with the mechanical exhaust equipment. The acccptahle kvel ufcontaminant rnnccntrations varies signi tirnntly from code lu code. A consensus on acceptahlc contaminant levels for enclosed parking garages is needed.

Un fortunately. Standard 62- l 9X9 does not address the issue of \entilation control through contaminant monitoring for enclosed garages. Thus. ASHRAE commissioned a rescard1 projeu (945-RP) to evaluate c urrent ventilation standards and recommend rates appropri:1te to current vehicle cmissions/usagt:.

Ventilation Regulation Tab/

ing codes and standard:-. for ventilating enclosed parking garages in the Unites States. and other selected wun tries. As shown in Tahli! I. the recommendations for the CO exposure limits arc not consistent bi.:twccn various regulations within the United Stares and other countries. Hm,\evcr. the recommendations offer an

indication of risks from exposure to CO in parking garages. A I imit of 25 ppm for hmg-tcm1 CO cxposure would meet almost every co

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ASHRAE Journal

foh!e ] summarizes somi:: of the results obtained during the field testing for sewn garages described in Ayari. ct al. (2000). The ACH Yalues present the range of the air changes per hnur mi::asurcd at various locations of the facility using the tracer gas technique, whik the L sm' (ctinilF) values provide the total ventilation rate.

TI1e maximum and the avernge ('()concentrntions measured during the day of testing arc listed in Tl.Ihle] to characterize the indoor quality within the tested parking facility. As indicated in fohlc ], the CO fcvd w ithin all the parking garngcs ne\ i.:r exceeded 35 ppm even though the wntilation rates in all c;iscs is well below the 7.62 L 'sm: ( 1.5 clin:tl') rewrrnrn:ndcd y Standard 62- I 9H9. The only garage that has a \ rnti lat ion rate ckit;e to 7 .62 l. sm: ( I . 5 c fm tF) is Garage E. which serv .. a large :,hopping mall with hca\ y usage throughout the day. It should be noted t hat all the garages ari.: wntilati.:d continuously except Garage B. whcri.: CO sensors were used to control the opera-

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(Circle No. 53 on Reader S.rvlce Card) 54 ASHRAE Journal

tion of thi.: supply fans. From the licld study. the

following results were obtained:

I. All the tcskd enclosed parking garages had Clln taminan t kvds that are signiticantly IO\ver than those n:quiri.:d by even the most stringent regulations (i.e. 25 ppm of8-hour weighted a\ eragi:: of CO concen1rntion).

2. The atual ventilation rates supplied lo the tested garagi::s were gencrJlly well below lhosi.: rccorrnm:nded by S tandard 62 - I 9Q ( i .e_, bi.:low 7.62 Usm' [1.5 ctin- n: n.

3. When it is us.:d. d.:mand .:ontrnlli.:d vi.:ntilation was ahk Ill maintain acu:ptable indoor air quality within the IL'sted enclosed parking facilities.

ASH RAE

ICBO

NIOSH/ OSHA

BOCA

SBCCI

NFPA

ACGIH

Canada

Finl and

France

Germany

Japan/Soutt Korea

Netherlandl!

Sweden

U.K.

nme (hrs) 8 1

8 ,

8 Ceiling

-

-

-

8

8 1

8 15 minutes

Ceiling 20 minutes

-

-

0.5

-

8 15 minutes

PPM Ventllatlon

9 7.6 Us m' 35 (1.5 cim!W)

50 7.6 Us m' 200 (1.5 cfm/ft')

35 -200

- 6ACH

- 6-7 ACH

- 6ACH

25 -

, 1 /13 -25/30

30 2.7 Us m: 75 (0.53 ctmift')

200 165 Us car 100 (350 cfm/car)

3.3 Us m' -(0.66 cfm!lt')

6 35-7.62 Lis m1 - (1 25-1.5 cfmfft")

200 -

0.91 Us m2 -(0.18 cfm/ft'-")

50 6-10 ACH 300

.The location of supply and exhaust \'Cills. traffic flow pattern, thi.: number of mov ing cars. and travel time ,ere important factors that affect thi.: effectiveness of the ventilation system in maintaining acceptable CO (or NO ) levels within enclosed ' park ing garages. Any des ign guiddines should account for thi.:sc lu:tors to determine the ventilation requirements for enclosed parking facilities.

Table 1: Summary of U.S. and international standards tor ventilation requirements of enclosed parking garages.

It is clear from the results of th.: field study that the current ventilation rate specified in Standard 62-1989 is outdated for endosed parking garages. New design guidelines are needed to providc the minimum ventilation mle required to maintain contaminant concentrations within parking facilities at the acceptable levels set by the relevant health authorities without large penalties in fan energy use. Guidelines should account for variability in the parking garage traffic flow. car emissions. travel time, and number of moving cars.

Design Approach Based on the results of scveral para-

metric analyses,' a simple design mi.:thod was developed lo detcnnine the entilat ion flow rate required 10 maintain aeccptable CO level within endosed parking facilities . Ventilation rates fi.ir cndoscd parking garages can be i.:xprcsscd in terms of either flow rate per unit floor area (L/sm: or cfmlff) or air volume changes per unit time (ACH). The design ventilation rati.: required for an enclosed parking facility depends on four factors:

I. Contaminant kvcl acccptahk within the parking facility:

2. Number of cars in operation during peak conditions:

3. Length oftnwe! and operation time www.as h raejo u rna I. o rg February 2001

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ASHRAE Journal

of c;:irs in the parking garage: and. .t. EmissiLln rate of a typical car under varitius conditions. Data for these factors shoulJ be av ai labk to deten11i111.: a'Cu

ratdy the design \ entilation rate tl>r enclosed parking gamges. A simple Jesign approach is pn:scnteJ in thi.: fol lO\v i ng section to detcnnine the requireJ ventilation rate tllr existing and nt.wly constrncted enclosed parking garages.

General Procedure for the Design Method To dctcrminc the required design flow rate to ventilate

an enclosed p